A plurality of systems are designed to detect movement of an element. Such systems typically utilize the detected movement information to synchronize other operations. By way of example, in an image forming device (e.g., printer, photocopier, facsimile machine, etc.), the detected movement information of media may, be used to synchronize the placement of image forming material onto the media.
The movement of a web of material may be detected through implementation of a pair of photosensors located a distance apart from each other along a feed direction. For instance, FIG. 1 (U.S. Pat. No. 6,118,132) depicts a system containing a pair of photosensors 16 and 18 that are located near the web of material and spaced a distance “d” apart from each other. In this system, a portion of the web of material is photographed by the first photosensor 16, fed a predetermined distance, and photographed by the second photosensor 18. By comparing the locations of the web portions in the respective photographed images, the movement of the web of material is determined.
The system is utilized for calculating velocity, displacement and/or strain of a moving web of material. The photosensors 16 and 18 detect an inherent structure-related property (such as paper fibers, or other constituents) of the web of material at various instances in time. By comparing the detected locations of the inherent structure-related property, the velocity, displacement and/or strain of the moving web of material is calculated.
However, if there is a change in speed of the web of material between the two images (for example, when the web is accelerating or decelerating), one of the images may have a greater level of distortion, e.g., blur or other forms of distortion, as compared to the other image. Thus, it may be difficult for an image recognition algorithm to operate in a relatively efficient manner. One solution is to reduce the time the exposure of a photosensor is open. However, the reduction in exposure time may require a higher amount of illumination in order to ensure that the images are properly illuminated. This increase in illumination may necessitate an associated increase in the cost of the imaging system and may, at a certain point, become impractical.